Bearings with force indicating means



Oct. 13, 11959v 2 Shets-Sheet 1 Filed Jan. 31, 1957 w J M M V m m 4 \N Jd L 7 r a W N WHNN \\m WM k a L ATTORNEYS M. J. BAMBER BEARINGS wrmFORCE INDICATING MEANS Filed Jan. 31, 1957 Oct. 13, 1959 2 Sheets-Sheet2 AN Q ma h J. W,

ATTORNEYS n tfi Rete Q- 2,908,164 p BEARINGS WITH FORCE INDICATING MEANSMillard J. 'Bamber, Washington, D.C., assignor to-the United States of'America as represented by the Secretary of the Navy 1 ApplicationJanuary 31, 1957 Serial No. 631,600

6 Claims. 01. 73-147 (Granted under Title 35, US. Code 1952), sec. 266)model in a wind tunnel and measuring the magnitude of forces on suchmodel. r

More specifically, this invention relates to the utilization of theprincipal of air-lubricated hearings in a sting- -type model-support andforce-indicating, system.

A number of systems, such as steelyards, balances, springs and the like,have been devised for supporting and measuring forces on aircraft modelsin wind tunnels. However, each of the known systems has certain inherentdisadvantages, such as being inaccurateand/or too complicated and bulky.I I

p A prime requisite of a sting-type model support isxthat it must berelatively small and simple so as to fit within an aircraft model andstill be capable of indicating forces and moments with the requiredaccuracy.

' A=principle object of thepresent invention is to provide a system forindicating the forces acting on 'an aircraft model more accurately thanis obtainable with heretofore known practical means.

A -furtherobject of this invention "is to provide'a support andforce-indicating system wherein forces on an object can be measuredwithprecision at 'a location remote from the 'objects j j A further objectof this invention is to'provide a support and force-indicating systemthat is relatively simple, compact and accurate.

A more specific object 'of the present invention is to provide a supportfor testing-model aircraft, which support is devoid of solid friction;

Applicant conceived that because of the frictionless characteristics ofair-lubricated bearings, theoretically The force-indicatingpossibilities arise from the fact that, under certain conditions, thepressure differential existing between opposite sides of an air bearingmust ,bear some relation to :the weight supported by the bearing,,ethatis, the load. In using such-atsystem'in tunnels as a modelsupport,especially thezst'ing-rnounted The practicability of using .theprinciple of air-lubri- .cated beaiingsdepends primarily upon theexactness with which :the difierential pressures .taken from. :thebearing correspond to the load. The theoryor principle ofpperm tion ofair-lubricated bearings is I wen known aw and need not be described indetail here.

-.the ends of ,two pairs A of a r-press n es 25 end-.2 e a i a h2,908,164 Oct. 13, 1959 "2 The invention, together with .the above .andother .objects and advantages ,.is set forth in-more technical detail inthe following description andaccompanying drawings, wherein: p I I Fig.1 is aside elevational view ofa stingiype model support incorporatingvthis inyentiona,

Fig. 2 is .a longitudinal section taken substantially on line 2-2 ofFig. 1 illustrating :a ball-and;socket type of air bearing with.amanometer remotely connected thereto;

.Fig. 3 is a transverse sectionrtaken on lined-$1015 Fig.2; p Fig. 4 is:a transverse section similar to that 20f Fig. 3, and taken on lineMoi-Fig.2; 1 o

Fig. 5 is a longitudinal section and ,partial elevation of the :flat-padtype -of air bearing, :shownat the leftend of Fig. 1, andhaving amanometer connectedihereto; Fig.6 is,a transverse section taken on;line'6 --.6 of Fig.5; V J; p 1 Fig. 7 is a side elevational .view-of-a.part of the bearing. shown, in Figs. 5 and 6 :and takenzsubstantiallyonline77ofF-ig.6. p Y 4 1 Referring now to Fig-,1 of the drawing whereinapreferred embodiment of the inventioncomprises vasting support,indicated by reference numeral :10, :upon whichis mounted .an aircraftmodel 12,..diagrammaticallyillustrated by broken .lines, all locatedwithin a'wind tunnel, not shown. 1v

The sting support includes .a hollow (steel member '14 rigidly mountedat the, right-hand end thereof .011- .a suit able support 16" within thetunnel. The .tubular member '14 is-closedateach end, except thata highpreS- sure air line 18 opens .into the right-hand end thereof.

Airline 18 supplies liigh-pressureair to su pport 1.4 from i a suitablesource, not shown. Tubular member. 14,

formed with an integral nipple or branch5section 14a,.in opencommunication .therewith, Which branch seotion is closed at itsouterend. Mounted on the supportpor tu- .bular member 14 are-three airlubricated bearings, 2Q,; 20, and 30. The construction and operation ofbearings 20 and 20 are substantially identical, sozthata detaileddescription of one such bearing With reference to 2, .3 and i4,' .bearing .20. inc1udes a sleeve or cylindrical member 21 having an interiordiameter slightly greater'than theexteriordiarnetenof, thetube 14 was toprovide a slightclearance. therebetween, which clearanceisexaggerated inFigs. 2-4. The exterior surface of sleeve 21 is formedwith asphericalportion 21a -u pon which is {mounted a ,collar 22, .whichcollar-is made of twoidentical halves for ease of assembly, and thecollar is formed with a concave portion 22a that coincides in contourwith the spherical portion 21a of sleeve 21,, thereby forming aball-and-socketjoint and a s elf-aligning-bearing. The sleeve 21 and.collar' ZZare each formed of brass, bronze or other suitable bearingmetal. ;,A rectangular steel plate ,23 having -a circular openingtherein is rigidly attached, as .by a press-fit, to the collar 22. In

practice the sleeve 21 collar 22 and rectangular platelfi are assembledas a unit and-then slipped ontotheiubular member-14.

As shown in Figs. .2 and 3, the ,ltnbular. ,supportgldzis formed withtwo setsof relatively small-radialairpo qts or pressure orifices 24 for;flow rofhigh pressure air from the interior of the support -tq-.the'.space;ibetween the support and the bearing 7 sleeve .21 :mountedthereon. For purpose of illustration, the -dameter of the pressureorifices 24 is exaggerated ginfii Figs. 2 and ,4,.the tubula r suppo e u-sp ed. r ial. a es there "r therrs sat n o P8 ordeadzou i p ed 1.opening in suppo .-s show in rme wit fou W25 fend i V Y 2,908,164 7 eachof'the air tubes iscount c rsunk, asshown in 4.

Each of the pairs of air tubes is carried through the sup-' port 14 to apoint withoutthe wind tunnel where they are each connected to suitabledifEerence-in-pressure indicator such for 'ex amplevasya manometer, 01?other type pressureindicator onto; a pressure recorder; Fig. '2,

diagrammatically shows theremote ends of tubes 25 con- 7 nected to amanometer 27. The remote ends of tubes 26 are connected 011 secondmanometer, not shown.

A rectangular steelplate- 28" is fitted in abutting 'r'elation with alower surface ofplate 23 and is rigidly attached to such plate by a pairof spaced set screws29, only' one pf-which screws ''-is shown in Fig. l.Plate28fis provided with a-circularopening thereinfoi"'thereceptiom'ias' by pressfit, of the cylindrical collar 22' ofair-lubricated bearing 20': *Be aring' 2'0'fis fitted' oritothetubularrnipple l4 a-of support 1 4 andfj s'tated heretofore, i s -ofthe same'jconstruction-as bearing 20, i --"-Refe rr in"gowt *FigsI5-7,air-lubricatedbearing?30, attached tofthe -le'ft nd (Fig.1) assupportlsL; includes a metal box-like member 31"havinga 'cylinder boreopen at the right-hand rend andsclosed at the left endf bore of'rnerhbcrflifishfsubstantially the same-diameter I which is shown inFig. 5), through the support to a point without the wind tunnel wherethey are connected to a difIerence-in-pressure indicator. 1 y

' In practice, the surfaces of the four bearing facesof member 31 and,the four individual pads 32 mustbe carefully finished, and opposing'pads, air supply ports, air lead-out ports and the like must be alikeor matchedif the calibration of the bearing is not to changewithairsupply pressure or change in the directionof the load on the'bearing.i

Each of the bearings 20, 20' and performsthe same function and thesebearings are in fact interchangeable. In certain installations, theround bearing, as 20 and 20, are more desirable; in other installationsthe square bearing 30 is more desirable; Whereas, in still otherinstallations, a combination of round and square bearings ap pears togive best results. I

With air-lubricated bearings, when a force is applied to the supportsystem, the component perpendicular to a bearing surface increases thegap orclearance on one side 7 and decreases the gap or clearance ontheother- 'or op- An airbearing has restraint in 'only one plane; the

plane perpendicular to the axis of the bearing. It is free to turn onand to move along the shaft. Thus if three bearing units like thoseshown in Fig. l'arerigidly posiprovided with a'lock' nut 36 and with'aball bearing 37,

which:ball bearing is held'in place'by a pair of dimples, 'onejformedin'the nd "of the adjusting screw and the 'o'therincenterofthe-respective pad- 32. For purpose of illustration, "the air''sp'ace-or clearance between the fiat faces sm aring member 31fa'nd the'pads 32 is exaggerateaaa-Figs; S and d; A- pair of set screws 38,threaded imdtappedopenings in the left end (Fig. l) of plate -28,- lioldframe member 34 rigidly {attached to such e; uz: is e Alsshdwn in'Figs'.5;a"nd"7;, a plurality of small .airsupply ports or 'orifices'ltliextendradially fromtheinterior 7 of support '14; through each 'of thetbpjbbttom and "two side faces of'box-like bearing member B'lQ'and theseorifices open-imo" "the clearance spaces between the 'f ace's of member31 and the fia t'padsBZI shows eight V such air ports in-one-ofjth'eside faces of member $1 and 'a-"like' number of ports is located in eachof the other races. However, as will be described" hereinafter, the

number and size of the airports depends upo n the use of the air'b'earing the air' pressure' supplied 'ther eto. p I p I j i The box-likebearing member'31' may be formed as an integral 'part of support;14fwith four equallyfspaced radial bores-therein for the receptionoftwopairs of air pressure -'taps" or le'ad-out tubes' thatarethe sameiin'construction 1 r and perform the s'ame"functihn as tubes Hand 26 ofFig's'g' 2 4 However, inthe specific embodiment of the 31 is formed as aseparate piece pneumatically-sealed to the'leift end of support14. -Asshown, each ofthe top, bottom and -s'ide faces of member 31 is providedwith 'centrally 'located insert41 having; an orifice 42 therein. -Thetop-and bottom orificesf 42 (Fig. '5) open into a pair of air,'lead-out'tubes 44,-the-entrance' ends of which airtubes-are"'pneumatically sealed-within a pair of di- 'ametri'callyopposite openings in support 14', and the 'remote ends'of whichair tubesextend through the support to a convenient location without the windtunnel where they are connected to a difference in-pressure indicatorsuch asa manometer 45- (Fig; 5) The two side orifices}...

open into alike pair of lead-out' tubes 46 (only oneof a on... a.) m

tioncd with respect/to each other in a framework on shafts with mutuallyparallel and perpendicular 'axis such as shown in Fig. l, the bearingassemblies will have no more motion. with respect to each other than'theclearance in the bearings. By locating the pressure taps shown in Figs.4 and 5 in planes mutually parallel and perpendicular to each other, theforces indicated by .the pressure diiferences can'be used to determinethe components of theresultant of the forces and moments applied to thesystem.

It is to be noted, in the illustrated embodiment of the invention, theair-lubricated bearings 20 and 30 areof themselves free to turn on andtomove longitudinally of the support 14. However, because oftheirconnection with plate 28, this longitudinal and rotary movement is'limited to the amount of clearanceflnot shown) provided betweenbranch,14a of the support and sleeve 21 of bearing 20-. Likewise,bearing 20' is of itself free to turn on and to move longitudinallyrelative to branch 14a. But these latter movements ;are limited by theclearance provided between support 14 and sleeve 21 of bearing '20 andby the likeclearanee'between member 31 and the pads 32 of bearing 30.:Thus, because of the interlock between bearings 20, 30 and 20, throughframes 23 and 34 "and plate 28, each of the bearingsror all practicalpurposes, is limited to movement inaplane perpendicular to the axis(transversely or radially of its support, which'movement is limited bypredetermined clearance.

In practice the maximum'load carrying capacity of the system dependsprincipally upon the area of the bearing with nochangein-operatingcharacteristics except for V load carrying capacity.Fromqtest results, there is no reason to believe that 'the'characteristics would be face fandgwith bearing'clearance inia rangeof;0.0005 to 0;00'1'0 inch. Howe /ten; performance-wise, there, appears,

which tubes likewise extend to be little if any relation between airpressure, load, airsupply orifice area and clearance.

In operation, an aircraft model 12 (Fig. 1) which is hollow is slippedover the left end of support 14 and is attached by suitable means, notshown, to plate 28 of the bearing system. Air, under relatively highpressure, is then supplied through conduit 18 to the interior of thetubular support 14, from whence the high pressure air flows through theair-supply ports 24 of bearing 20, 24 (not shown) of bearing and 40 ofbearing 30, into the clearance spaces of each of the bearings, whereuponeach of the bearings with the model supported thereby is supported by afilm of relatively static high pressure air. Assuming that the separatepairs of air lead-out tubes 25 and 26 of bearing 20, 25' and 26' (notshown) of bear-- ing 20' and 44 and 46 of bearing are connected tosuitable pressure diiferential gauges, such as manometers 27 and 45 ofFigs. 2 and 5, a reading of the gauges will show the pressuredifferences and thus the loads on opposite sides of the bearings.

Assuming for descriptive purpose of force direction that Fig. 1 is aside elevational view of the support'with the model attached thereto,although this figure might just as well be a top or a bottom plan viewof the support, forces and components thereof that operate in oppositedirections in three major planes may be read on the pressuredifferential gauges or recorded on a suitable recorder. That is, thegauges remotely connected to the lead-out tubes of bearing 20 willindicate differences in pressure to forces and their components actingvertically upward and vertically downward in planes parallel to thepaper, and horizontal forces inward and outward in planes perpendicularto the paper. The gauges connected to the lead-out tubes of bearing 30will indicate differences in pressure of forces and their components indirections generally the same as those of bearing 20. The

gauges connected to the lead-out tubes of bearing 20' will indicatedifierences in pressure of horizontal, transverse forces and theircomponents inward and outward in planes perpenidcular to the plane ofthe paper and horizontal, longitudinal forces and their components fromthe left and the right in planes parallel to the plane of the papers.Thus the resultant of three principal forces and their components may beascertained, from which the principal moments may be calculated.

Without further description, it is thought that the novel features andadvantages of the invention will be readily apparent to those skilled inthe art to which the invention appertains, and it will, of course, beunderstood that changes in form, proportions and minor details ofconstruction may be resorted to without departing from the spirit of theinvention and scope of the claims.

What is claimed is:

1. An apparatus for measuring component forces and moments developed byrelative motion of a hollow test model in a fluid medium, said apparatuscomprising a sting-type tubular support, means for supplying air underrelatively high pressure to the interior of the support, bearing meansfor supporting the test model on the support for limited movement of themodel relative to the support, said support and said bearing meansfitting olf tubes leading from diametrically opposite sides oftheclearance space through the tubular support to a point remote from thesupport, and pressure dilferential indicating means connected to theremote ends of the tap-off tubes.

2. An apparatus as set forth in claim 1 wherein the air-lubricatedbearing includes an interior surface of substantially the samecross-sectional shape as that portion of the exterior surface of thesupport upon which the bearing is mounted.

3. An apparatus as set forth in claim 1 wherein the tubular supportincludes a cylindrical exterior surface, wherein the air-lubricatedbearing includes a sleeve having a cylindrical interior surface ofsubstantially the same contour as the cylindrical exterior surface ofthe support, and wherein the clearance space is circular in crosssection.

4. An apparatus as set forth in claim 3 wherein the plurality ofair-supply ports radiate in substantially uniform spaced relation fromthe interior of the tubular support to the circular clearance spacethroughout the circumference thereof, and wherein the plurality ofpressure tap-off tubes includes four tubes leading from uniformly spacedpoints of the circular clearance space with diametrically opposite tubesof each pair of tubes connected to one of the pressure differentialindicating means.

5. An apparatus as set forth in claim 1 wherein the tubular supportincludes four flat faces uniformly spaced around a circumferencethereof, wherein the air-lubricated bearing includes four flat pads withone of such pads supported in spaced relation to each of the four flatfaces of the tubular support, wherein the plurality of air supply portsis equally divided between the four flat faces of the tubular support,and wherein one of the plurality of pressure tap-off tubes leadscentrally from each of the four flat pads.

6. An apparatus as set forth in claim 1 wherein the bearing meansincludes three air-lubricated bearings mounted on exterior portions ofthe support each in spaced relation thereto with two of the bearingsmounted on a common axis parallel to the longitudinal axis of thetubular support and with the third of the bearings mounted on an axisperpenidcular to the said common axis, and means connecting said threebearings to each other for limited unitary movement relative to thesupport.

References Cited in the file of this patent UNITED STATES PATENTS

